Polo Grounds III was the stadium that made the name nationally famous. Built in 1890, it initially had a completely open outfield bounded by just the outer fence, but bleachers were gradually added. By the early 1900s, some bleacher sections encroached on the field from the foul lines about halfway along left and right field. Additionally, there was a pair of "cigar box" bleachers on either side of the "batter's eye" in center field. The expansive outfield was cut down somewhat by a rope fence behind which carriages (and early automobiles) were allowed to park. By 1910, bleachers enclosed the outfield, and the carriage ropes were gone. The hodge-podge approach to the bleacher construction formed a multi-faceted outfield area. There were a couple of gaps between some of the sections, and that would prove significant in 1911.

Known as Brotherhood Park when it opened in 1890, Polo Grounds III was the home of a second New York Giants franchise in the Players' League. The latter was a creation of Major League Baseball's first union, the Brotherhood of Professional Base-Ball Players. After failing to win concessions from National League owners, the Brotherhood founded its own league in 1890. The Players' League Giants built Brotherhood Park in the northern half of Coogan's Hollow, next door to Polo Grounds II, otherwise bounded by rail yards and the bluff. Brotherhood Park hosted its first game on April 19, 1890, the same day the National League's Giants played their first home game of the season. For the full 1890 season the two editions of the Giants were neighbors. When the teams played on the same day, fans in the upper decks could watch each other's games, and home run balls hit in one park might land on the other team's playing field. After the one season the Players' League folded, and the Brotherhood's members went back to the National League. The National League Giants then moved out of Polo Grounds II and into Brotherhood Park, which was larger. They took their stadium's name with them once again, turning Brotherhood Park into the new-new Polo Grounds. Between Polo Grounds II and III-IV, they would remain in Coogan's Hollow for 69 seasons.

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